------- Additional Comments From aoliva at gcc dot gnu dot org 2005-03-10
11:44 -------
Subject: Re: [PR target/20126, RFC] loop DEST_ADDR biv replacement may fail
On Mar 9, 2005, Jakub Jelinek <[EMAIL PROTECTED]> wrote:
> On Wed, Mar 09, 2005 at 01:02:08AM -0300, Alexandre Oliva wrote:
>> On Mar 8, 2005, Jakub Jelinek <[EMAIL PROTECTED]> wrote:
>>
>> > Unfortunately, it seems to break ada bootstrap on at least x86-64 and i386:
>>
>> Odd... It surely completed bootstrap for me with default build flags.
> Your code hits just once on ali.adb
Rats, I didn't realize I needed --enable-languages=all,ada to pick
that up. Fixed now.
> Note that recog_memoized (v->insn) is -1 even without the change,
> not sure what would fix that up.
Problem is that the insn has a volatile memory access, and loop runs
with volatile_ok = 0.
I'm not entirely sure why that is; presumably to avoid introducing or
removing volatile memory accesses. I can see how this prevents
introducing them, but it appears to me that it still can remove them.
Anyhow, I've come up with a solution for this. This patch introduces
a new function that is like validate_change, but if validate_change
fails and the original insn fails to be recognized with !volatile_ok
but passes with volatile_ok, then try the change and recog with
volatile_ok.
> But it certainly shows that *v->location doesn't have to be
> a simple pseudo, so gen_move_insn might not work.
Indeed. I've introduced a new pseudo to hold the computed value now,
for the case in which *v->location isn't a reg.
Passed bootstrap and regtest on x86_64-linux-gnu on mainline, as well
as bootstrap on gcc-4_0-rhl-branch, both with Ada enabled. Ok to
install?
Index: gcc/ChangeLog
from Alexandre Oliva <[EMAIL PROTECTED]>
PR target/20126
* loop.c (loop_givs_rescan): If replacement of DEST_ADDR failed,
set the original address pseudo to the correct value before the
original insn, if possible, and leave the insn alone, otherwise
create a new pseudo, set it and replace it in the insn.
* recog.c (validate_change_maybe_volatile): New.
* recog.h (validate_change_maybe_volatile): Declare.
Index: gcc/loop.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/loop.c,v
retrieving revision 1.522
diff -u -p -r1.522 loop.c
--- gcc/loop.c 17 Jan 2005 08:46:15 -0000 1.522
+++ gcc/loop.c 10 Mar 2005 11:23:59 -0000
@@ -5470,9 +5470,31 @@ loop_givs_rescan (struct loop *loop, str
mark_reg_pointer (v->new_reg, 0);
if (v->giv_type == DEST_ADDR)
- /* Store reduced reg as the address in the memref where we found
- this giv. */
- validate_change (v->insn, v->location, v->new_reg, 0);
+ {
+ /* Store reduced reg as the address in the memref where we found
+ this giv. */
+ if (validate_change_maybe_volatile (v->insn, v->location,
+ v->new_reg))
+ /* Yay, it worked! */;
+ /* Not replaceable; emit an insn to set the original
+ giv reg from the reduced giv. */
+ else if (REG_P (*v->location))
+ loop_insn_emit_before (loop, 0, v->insn,
+ gen_move_insn (*v->location,
+ v->new_reg));
+ else
+ {
+ /* If it wasn't a reg, create a pseudo and use that. */
+ rtx reg, seq;
+ start_sequence ();
+ reg = force_reg (v->mode, *v->location);
+ seq = get_insns ();
+ end_sequence ();
+ loop_insn_emit_before (loop, 0, v->insn, seq);
+ gcc_assert (validate_change_maybe_volatile (v->insn, v->location,
+ reg));
+ }
+ }
else if (v->replaceable)
{
reg_map[REGNO (v->dest_reg)] = v->new_reg;
Index: gcc/recog.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/recog.c,v
retrieving revision 1.221
diff -u -p -r1.221 recog.c
--- gcc/recog.c 7 Mar 2005 13:52:08 -0000 1.221
+++ gcc/recog.c 10 Mar 2005 11:24:01 -0000
@@ -235,6 +235,34 @@ validate_change (rtx object, rtx *loc, r
return apply_change_group ();
}
+/* Same as validate_change, but doesn't support groups, and it accepts
+ volatile mems if they're already present in the original insn.
+
+ ??? Should this should search new for new volatile MEMs and reject
+ them? */
+
+int
+validate_change_maybe_volatile (rtx object, rtx *loc, rtx new)
+{
+ int result;
+
+ if (validate_change (object, loc, new, 0))
+ return 1;
+
+ if (volatile_ok || ! insn_invalid_p (object))
+ return 0;
+
+ volatile_ok = 1;
+
+ gcc_assert (! insn_invalid_p (object));
+
+ result = validate_change (object, loc, new, 0);
+
+ volatile_ok = 0;
+
+ return result;
+}
+
/* This subroutine of apply_change_group verifies whether the changes to INSN
were valid; i.e. whether INSN can still be recognized. */
Index: gcc/recog.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/recog.h,v
retrieving revision 1.55
diff -u -p -r1.55 recog.h
--- gcc/recog.h 7 Mar 2005 13:52:09 -0000 1.55
+++ gcc/recog.h 10 Mar 2005 11:24:01 -0000
@@ -74,6 +74,7 @@ extern void init_recog_no_volatile (void
extern int check_asm_operands (rtx);
extern int asm_operand_ok (rtx, const char *);
extern int validate_change (rtx, rtx *, rtx, int);
+extern int validate_change_maybe_volatile (rtx, rtx *, rtx);
extern int insn_invalid_p (rtx);
extern void confirm_change_group (void);
extern int apply_change_group (void);
Index: gcc/testsuite/ChangeLog
from Alexandre Oliva <[EMAIL PROTECTED]>
* gcc.dg/pr20126.c: New.
Index: gcc/testsuite/gcc.dg/pr20126.c
===================================================================
RCS file: gcc/testsuite/gcc.dg/pr20126.c
diff -N gcc/testsuite/gcc.dg/pr20126.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ gcc/testsuite/gcc.dg/pr20126.c 10 Mar 2005 11:24:16 -0000
@@ -0,0 +1,50 @@
+/* dg-do run */
+/* dg-options "-O2" */
+
+/* PR target/20126 was not really target-specific, but rather a loop's
+ failure to take into account the possibility that a DEST_ADDR giv
+ replacement might fail, such as when you attempt to replace a REG
+ with a PLUS in one of the register_operands of cmpstrqi_rex_1. */
+
+extern void abort (void);
+
+typedef struct { int a; char b[3]; } S;
+S c = { 2, "aa" }, d = { 2, "aa" };
+
+void *
+bar (const void *x, int y, int z)
+{
+ return (void *) 0;
+}
+
+int
+foo (S *x, S *y)
+{
+ const char *e, *f, *g;
+ int h;
+
+ h = y->a;
+ f = y->b;
+ e = x->b;
+
+ if (h == 1)
+ return bar (e, *f, x->a) != 0;
+
+ g = e + x->a - h;
+ while (e <= g)
+ {
+ const char *t = e + 1;
+ if (__builtin_memcmp (e, f, h) == 0)
+ return 1;
+ e = t;
+ }
+ return 0;
+}
+
+int
+main (void)
+{
+ if (foo (&c, &d) != 1)
+ abort ();
+ return 0;
+}
--
Alexandre Oliva http://www.ic.unicamp.br/~oliva/
Red Hat Compiler Engineer [EMAIL PROTECTED], gcc.gnu.org}
Free Software Evangelist [EMAIL PROTECTED], gnu.org}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20126
